1. Field of the Invention
The present invention relates to a method of adjusting a limiting value of an operating temperature of a cooking unit, which has a glass or glass-ceramic cooking surface with at least one heated cooking zone. The invention also relates to a device for performing the method.
2. Prior Art
The glass-ceramic material for a modern cooking unit with a glass-ceramic cooking surface is made by a temperature/time treatment of a special glass. Among other things, the thermal expansion behavior is adjusted for the application. If impermissibly high temperature/time loads occur in usage, among other things, the reduced thermal expansion behavior is lost and, in extreme cases, the glass-ceramic material can fail or break.
Analogously this is also true for a cooking unit, which uses thermally or chemically pre-stressed glass. At a high operating temperature this leads to a loss of the pre-stressing, which can lead to destruction of the product.
In cooking units of the above-described kind according to the state of the art temperature monitoring of the glass/glass-ceramic cooking surface is provided by means of an operating temperature limiting device, which is adjusted so that the permissible temperature/time load on the glass/glass-ceramic cooking surface during the required operating life at a nominal operating frequency is not exceeded. A guideline or directive for the operating frequency has been published in German Standard DIN VDE 0700, Part 6, Appendix 8.
A mechanical operating temperature limiting device with a solid expansion controller is known. Also an electronic operating temperature limiting device is known. A conductor strip directly mounted on the cooking surface (as in DE 40 22 846 C2) or a discrete platinum temperature-measuring resistor (as in DE 37 36 005 A1) can be used as a sensor for this electronic operating temperature limiting device. However these electronic operating temperature limiting devices according to the state of the art--just as the corresponding mechanical operating temperature limiting devices--are always calibrated or adjusted to a fixed temperature limiting value and shut off the heating of the respective cooking zone, as soon as the set boundary or limiting value of the operating temperature, also the so-called shut-off temperature, has been reached.
These operating temperature limiting devices thus monitor the temperatures occurring in the cooking unit so that no impermissible change of the glass/glass-ceramic material occurs within the predetermined lifetime.
The usage frequency of the cooking unit differs from household to household according to different lifestyles. The above-mentioned standard for the operating frequency for safety of the user produces a comparatively high load with frequent cooking. In the current state of the art the given value for the operating frequency and the limiting value of the operating temperature determined from that lead to the disadvantage that the user who operates the cooking unit with reduced operating time cannot use the available permissible temperature/time load, i.e. the full potential of the cooking unit in regard to the ability of the glass/glass-ceramic cooking surface to withstand a load. It would be permissible for an operator who runs the cooking unit with reduced operating time to use a higher operating temperature for individual cooking events so that the cooking time for those individual events can be reduced.
If the user only uses an easy-to-use cooking utensil or if the utensil is empty, the given temperature/time load cannot be utilized. Also here the full potential of the glass-ceramic cooking surface cannot be used.